1. Field of the Invention
The present invention relates to a device for feeding gas into a melt of foamable metal by means of a pipe to produce metal foam.
The invention further relates to a process for producing metal foam by blowing gas into a foamable metal melt.
2. Discussion of Background Information
Materials having new property profiles are increasingly required in innovative technology. Metal foam represents such a material. On the one hand, in comparison with a solid material, it has a substantially lower specific gravity, and on the other hand it shows different mechanical properties and a completely different material behavior.
Various processes are known for producing metal foam materials. For example, substances can be added to a metal melt and distributed therein, which substances disintegrate at the given melting temperature of the metal phase with concomitant gas development. The forming or formed gas bubbles are thereby frozen within the melt and a foam part is produced in this way.
Foaming processes are further known in which gas is fed beneath the surface of a melted, foamable metal, a so-called liquid composite material, and thereby a metal foam is produced. For example, such a continuous foaming process is known from WO 91/01387 and EP 483184 B1.
According to EP 545957 B1 an introduction of gas into a liquid metal can also be effected by means of a vortex. As a result thereof, pores of different diameters are contained in the foam material formed and solidified in this manner, resulting in a scarcely reproducible material behavior. An adjustment of the pore size or size distribution in the foam part is not thereby possible to a sufficient extent.
According to U.S. Pat. No. 5,281,251, gas is introduced into a melt by means of a feed device which has a blunger form and features gas discharge points on the outside blade ends. A similar embodiment of the gas introduction means or a vibrating or oscillating nozzle is disclosed in U.S. Pat. No. 5,334,236.
In order to achieve an efficient foam formation, it has also been suggested (EP-544291 A1) to add the gas to the liquid metal via a plurality of nozzles in the form of an oscillating nozzle comb or by means of a vertical nozzle with a rotating, propeller-like agitator above it for swirling the gas bubbles.
The entire disclosures of all of the above-referenced documents are expressly incorporated herein by reference.
All of the known devices for producing metal foam by blowing gas into a melt are disadvantageous in that they have in common that pores or gas bubbles with large differences in dimensions are formed and that their size and size distribution cannot be controlled to the desired extent. This often results in undesirable relatively high specific gravities and insufficiently reproducible material behavior of the metal foam material.